1. PowerPoint ® Lecture Slides prepared by Karen Dunbar Kareiva Ivy Tech Community College © Annie Leibovitz/Contact Press Images Chapter 11 Part C Fundamentals of the Nervous System and Nervous Tissue © 2016 Pearson Education, Inc.

2. 11.7 The Synapse Nervous system works because information flows from neuron to neuron Neurons are functionally connected by synapses, junctions that mediate information transfer –From one neuron to another neuron –Or from one neuron to an effector cell © 2016 Pearson Education, Inc.

3. 11.7 The Synapse Presynaptic neuron: neuron conducting impulses toward synapse (sends information) Postsynaptic neuron: neuron transmitting electrical signal away from synapse (receives information) –In PNS may be a neuron, muscle cell, or gland cell Most function as both © 2016 Pearson Education, Inc.

4. Figure 11.15 Synapses. © 2016 Pearson Education, Inc. Axon of presynaptic neuron Synapses Cell body (soma) of postsynaptic neuron

5. 11.7 The Synapse Synaptic connections –Axodendritic: between axon terminals of one neuron and dendrites of others –Axosomatic: between axon terminals of one neuron and soma (cell body) of others –Less common connections: Axoaxonal (axon to axon) Dendrodendritic (dendrite to dendrite) Somatodendritic (dendrite to soma) –Two main types of synapses: Chemical synapse Electrical synapse © 2016 Pearson Education, Inc.

6. Figure 11.16 Axodendritic, axosomatic, and axoaxonal synapses. © 2016 Pearson Education, Inc. Axosomatic synapses Axodendritic synapses Dendrites Cell body Axoaxonal synapses Axon

7. Chemical Synapses Most common type of synapse Specialized for release and reception of chemical neurotransmitters Typically composed of two parts –Axon terminal of presynaptic neuron: contains synaptic vesicles filled with neurotransmitter –Receptor region on postsynaptic neuron’s membrane: receives neurotransmitter Usually on dendrite or cell body –Two parts separated by fluid-filled synaptic cleft Electrical impulse changed to chemical across synapse, then back into electrical © 2016 Pearson Education, Inc.

8. Chemical Synapses (cont.) Transmission across synaptic cleft –Synaptic cleft prevents nerve impulses from directly passing from one neuron to next –Chemical event (as opposed to an electrical one) –Depends on release, diffusion, and receptor binding of neurotransmitters –Ensures unidirectional communication between neurons © 2016 Pearson Education, Inc.

9. Chemical Synapses (cont.) Information transfer across chemical synapses –Six steps are involved: 1. AP arrives at axon terminal of presynaptic neuron 2. Voltage-gated Ca 2+ channels open, and Ca 2+ enters axon terminal –Ca 2+ flows down electrochemical gradient from ECF to inside of axon terminal © 2016 Pearson Education, Inc.

10. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Postsynaptic neuron 1 Slide 2

11. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Voltage-gated Ca 2  channels open and Ca 2  enters the axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Postsynaptic neuron 1 2 Slide 3

12. Chemical Synapses (cont.) 3. Ca 2+ entry causes synaptic vesicles to release neurotransmitter Ca 2+ causes synaptotagmin protein to react with SNARE proteins that control fusion of synaptic vesicles with axon membrane Fusion results in exocytosis of neurotransmitter into synaptic cleft The higher the impulse frequency, the more vesicles exocytose, leading to a greater effect on the postsynaptic cell © 2016 Pearson Education, Inc.

13. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Voltage-gated Ca 2  channels open and Ca 2  enters the axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Ca 2  entry causes synaptic vesicles to release neurotransmitter by exocytosis. Postsynaptic neuron 1 2 3 Slide 4

14. Chemical Synapses (cont.) 4. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane Often chemically gated ion channels 5. Binding of neurotransmitter opens ion channels, creating graded potentials Binding causes receptor protein to change shape, which causes ion channels to open –Causes a graded potential in postsynaptic cell »Can be an excitatory or inhibitory event –Some receptor proteins are also ion channels © 2016 Pearson Education, Inc.

15. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Voltage-gated Ca 2  channels open and Ca 2  enters the axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Ca 2  entry causes synaptic vesicles to release neurotransmitter by exocytosis. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. Postsynaptic neuron 1 2 3 4 Slide 5

16. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Voltage-gated Ca 2  channels open and Ca 2  enters the axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Ca 2  entry causes synaptic vesicles to release neurotransmitter by exocytosis. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. Postsynaptic neuron Graded potential Binding of neurotransmitter opens ion channels, resulting in graded potentials. Ion movement 1 2 3 4 5 Slide 6

17. Chemical Synapses (cont.) 6. Neurotransmitter effects are terminated As long as neurotransmitter is binding to receptor, graded potentials will continue, so process needs to be regulated Within a few milliseconds, neurotransmitter effect is terminated in one of three ways –Reuptake by astrocytes or axon terminal –Degradation by enzymes –Diffusion away from synaptic cleft © 2016 Pearson Education, Inc.

18. Focus Figure 11.3 Chemical synapses transmit signals from one neuron to another using neurotransmitters. © 2016 Pearson Education, Inc. Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. Voltage-gated Ca 2  channels open and Ca 2  enters the axon terminal. Ca 2  Mitochondrion Ca 2  Synaptic cleft Axon terminal Synaptic vesicles Ca 2  entry causes synaptic vesicles to release neurotransmitter by exocytosis. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. Postsynaptic neuron Graded potential Reuptake Enzymatic degradation Diffusion away from synapse Binding of neurotransmitter opens ion channels, resulting in graded potentials. Neurotransmitter effects are terminated by reuptake through transport proteins, enzymatic degradation, or diffusion away from the synapse. Ion movement 1 2 3 4 5 6 Slide 7

19. Chemical Synapses (cont.) Synaptic delay –Time needed for neurotransmitter to be released, diffuse across synapse, and bind to receptors Can take anywhere from 0.3 to 5.0 ms –Synaptic delay is rate-limiting step of neural transmission Transmission of AP down axon can be very quick, but synapse slows transmission to postsynaptic neuron down significantly Not noticeable, because these are still very fast © 2016 Pearson Education, Inc.

20. Electrical Synapses Less common than chemical synapses Neurons are electrically coupled –Joined by gap junctions that connect cytoplasm of adjacent neurons –Communication is very rapid and may be unidirectional or bidirectional –Found in some brain regions responsible for eye movements or hippocampus in areas involved in emotions and memory –Most abundant in embryonic nervous tissue © 2016 Pearson Education, Inc.

21. 11.8 Postsynaptic Potentials Neurotransmitter receptors cause graded potentials that vary in strength based on: –Amount of neurotransmitter released –Time neurotransmitter stays in cleft Depending on effect of chemical synapse, there are two types of postsynaptic potentials –EPSP: excitatory postsynaptic potentials –IPSP: inhibitory postsynaptic potentials © 2016 Pearson Education, Inc.

22. Excitatory Synapses and EPSPs Neurotransmitter binding opens chemically gated channels –Allows simultaneous flow of Na + and K + in opposite directions Na + influx greater than K + efflux, resulting in local net graded potential depolarization called excitatory postsynaptic potential (EPSP) EPSPs trigger AP if EPSP is of threshold strength –Can spread to axon hillock and trigger opening of voltage-gated channels, causing AP to be generated © 2016 Pearson Education, Inc.

23. Figure 11.17a Postsynaptic potentials can be excitatory or inhibitory. © 2016 Pearson Education, Inc. Excitatory postsynaptic potential (EPSP) Membrane potential (mV)  30 0 An EPSP is a local depolarization of the postsynaptic membrane. EPSPs bring the neuron closer to AP threshold. Threshold  55  70 Stimulus 102030 Time (ms) Neurotransmitter binding opens chemically gated ion channels, allowing Na  and K  to pass simultaneously.

24. Inhibitory Synapses and IPSPs Neurotransmitter binding to receptor opens chemically gated channels that allow entrance/exit of ions that cause hyperpolarization –Makes postsynaptic membrane more permeable to K + or Cl – If K + channels open, it moves out of cell If Cl – channels open, it moves into cell –Reduces postsynaptic neuron’s ability to produce an action potential Moves neuron farther away from threshold (makes it more negative) © 2016 Pearson Education, Inc.

25. Figure 11.17b Postsynaptic potentials can be excitatory or inhibitory. © 2016 Pearson Education, Inc. Inhibitory postsynaptic potential (IPSP) Membrane potential (mV)  30 0 An IPSP is a local hyperpolarization of the postsynaptic membrane. IPSPs drive the neuron away from AP threshold. Threshold  55  70 Stimulus 102030 Time (ms) Neurotransmitter binding opens chemically gated ion channels permeable to either K  or Cl .

26. Integration and Modification of Synaptic Events Summation by the postsynaptic neuron –A single EPSP cannot induce an AP, but EPSPs can summate (add together) to influence postsynaptic neuron IPSPs can also summate –Most neurons receive both excitatory and inhibitory inputs from thousands of other neurons Only if EPSPs predominate and bring to threshold will an AP be generated –Two types of summations: temporal and spatial © 2016 Pearson Education, Inc.

27. Integration and Modification of Synaptic Events (cont.) –Temporal summation One or more presynaptic neurons transmit impulses in rapid-fire order –First impulse produces EPSP, and before it can dissipate another EPSP is triggered, adding on top of first impulse –Spatial summation Postsynaptic neuron is stimulated by large number of terminals simultaneously –Many receptors are activated, each producing EPSPs, which can then add together © 2016 Pearson Education, Inc.

28. Membrane potential (mV) Figure 11.18a Neural integration of EPSPs and IPSPs. © 2016 Pearson Education, Inc. E1E1 0 Threshold of axon of postsynaptic neuron Resting potential  55  70 E1E1 E1E1 Time No summation: 2 stimuli separated in time cause EPSPs that do not add together. Excitatory synapse 1 (E 1 ) Excitatory synapse 2 (E 2 ) Inhibitory synapse (I 1 )

29. Figure 11.18b Neural integration of EPSPs and IPSPs. © 2016 Pearson Education, Inc. E1E1 0  55  70 Excitatory synapse 1 (E 1 ) E1E1 Time Temporal summation: 2 excitatory stimuli close in time cause EPSPs that add together. Excitatory synapse 2 (E 2 ) Inhibitory synapse (I 1 ) E1E1 Membrane potential (mV)

30. Figure 11.18c Neural integration of EPSPs and IPSPs. © 2016 Pearson Education, Inc. E1E1 E2E2 0  55  70 E 1  E 2 Time Spatial summation: 2 simultaneous stimuli at different locations cause EPSPs that add together. Excitatory synapse 1 (E 1 ) Excitatory synapse 2 (E 2 ) Inhibitory synapse (I 1 ) Membrane potential (mV)

31. Figure 11.18d Neural integration of EPSPs and IPSPs. © 2016 Pearson Education, Inc. E1E1 I1I1 0  55  70 I1I1 E 1  I 1 Time Spatial summation of EPSPs and IPSPs: Changes in membrane potential can cancel each other out. Excitatory synapse 1 (E 1 ) Excitatory synapse 2 (E 2 ) Inhibitory synapse (I 1 ) Membrane potential (mV)

32. Integration and Modification of Synaptic Events (cont.) Synaptic potentiation –Repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron Ca 2+ concentration increases in presynaptic terminal, causing release of more neurotransmitter Leads to more EPSPs in postsynaptic neuron –Potentiation can cause Ca 2+ voltage gates to open on postsynaptic neuron Ca 2+ activates kinase enzymes, leading to more effective response to subsequent stimuli –Long-term potentiation: learning and memory © 2016 Pearson Education, Inc.

33. Integration and Modification of Synaptic Events (cont.) Presynaptic inhibition –Release of excitatory neurotransmitter by one neuron is inhibited by another neuron via an axoaxonal synapse –Less neurotransmitter is released, leading to smaller EPSPs © 2016 Pearson Education, Inc.

34. Table 11.2-1 Comparison of Graded Potentials and Action Potentials © 2016 Pearson Education, Inc.

35. Table 11.2-2 Comparison of Graded Potentials and Action Potentials (continued) © 2016 Pearson Education, Inc.

36. Table 11.2-3 Comparison of Graded Potentials and Action Potentials (continued) © 2016 Pearson Education, Inc.

37. Table 11.2-4 Comparison of Graded Potentials and Action Potentials (continued) © 2016 Pearson Education, Inc.

38. 11.9 Neurotransmitters Language of nervous system 50 or more neurotransmitters have been identified Most neurons make two or more neurotransmitters –Neurons can exert several influences Usually released at different stimulation frequencies Classified by: –Chemical structure –Function © 2016 Pearson Education, Inc.

39. Classification of Neurotransmitters by Chemical Structure Acetylcholine (ACh) –First identified and best understood –Released at neuromuscular junctions Also used by many ANS neurons and some CNS neurons –Synthesized from acetic acid and choline by enzyme choline acetyltransferase –Degraded by enzyme acetylcholinesterase (AChE) © 2016 Pearson Education, Inc.

40. Classification of Neurotransmitters by Chemical Structure (cont.) Biogenic amines –Catecholamines Dopamine, norepinephrine (NE), and epinephrine: made from the amino acid tyrosine –Indolamines Serotonin: made from the amino acid tryptophan Histamine: made from the amino acid histidine –All widely used in brain: play roles in emotional behaviors and biological clock –Used by some ANS motor neurons Especially NE –Imbalances are associated with mental illness © 2016 Pearson Education, Inc.

41. Classification of Neurotransmitters by Chemical Structure (cont.) Amino acids –Amino acids make up all proteins: therefore, it is difficult to prove which are neurotransmitters –Amino acids that are proven neurotransmitters Glutamate Aspartate Glycine GABA: gamma (  )-aminobutyric acid © 2016 Pearson Education, Inc.

42. Classification of Neurotransmitters by Chemical Structure (cont.) Peptides (neuropeptides) –Strings of amino acids that have diverse functions Substance P –Mediator of pain signals Endorphins –Beta endorphin, dynorphin, and enkephalins: act as natural opiates; reduce pain perception Gut-brain peptides –Somatostatin and cholecystokinin play a role in regulating digestion © 2016 Pearson Education, Inc.

43. Classification of Neurotransmitters by Chemical Structure (cont.) Purines –Monomers of nucleic acids that have an effect in both CNS and PNS ATP, the energy molecule, is now considered a neurotransmitter Adenosine is a potent inhibitor in brain –Caffeine blocks adenosine receptors Can induce Ca 2+ influx in astrocytes © 2016 Pearson Education, Inc.

44. Classification of Neurotransmitters by Chemical Structure (cont.) Gases and lipids –Gasotransmitters Nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide gases (H 2 S) Bind with G protein–coupled receptors in brain Lipid soluble and are synthesized on demand NO involved in learning and formation of new memories, as well as brain damage in stroke patients, and smooth muscle relaxation in intestine H 2 S acts directly on ion channels to alter function © 2016 Pearson Education, Inc.

45. Classification of Neurotransmitters by Chemical Structure (cont.) –Endocannabinoids Act at same receptors as THC (active ingredient in marijuana) Most common G protein–linked receptors in brain Lipid soluble Synthesized on demand Believed to be involved in learning and memory May be involved in neuronal development, controlling appetite, and suppressing nausea © 2016 Pearson Education, Inc.

46. Classification of Neurotransmitters by Function Neurotransmitters exhibit a great diversity of functions Functions can be grouped into two classifications: –Effects –Actions © 2016 Pearson Education, Inc.

47. Classification of Neurotransmitters by Function (cont.) Effects: excitatory versus inhibitory –Neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyperpolarizing) –Effect determined by receptor to which it binds GABA and glycine are usually inhibitory Glutamate is usually excitatory Acetylcholine and NE bind to at least two receptor types with opposite effects –ACh is excitatory at neuromuscular junctions in skeletal muscle –ACh is inhibitory in cardiac muscle © 2016 Pearson Education, Inc.

48. Classification of Neurotransmitters by Function (cont.) Actions: direct versus indirect –Direct action: neurotransmitter binds directly to and opens ion channels Promotes rapid responses by altering membrane potential Examples: ACh and amino acids –Indirect action: neurotransmitter acts through intracellular second messengers, usually G protein pathways Broader, longer-lasting effects similar to hormones Biogenic amines, neuropeptides, and dissolved gases © 2016 Pearson Education, Inc.

49. Classification of Neurotransmitters by Function (cont.) Actions: direct versus indirect (cont.) –Neuromodulator: chemical messenger released by neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission May influence synthesis, release, degradation, or reuptake of neurotransmitter May alter sensitivity of the postsynaptic membrane to neurotransmitter. May be released as a paracrine –Effect is only local © 2016 Pearson Education, Inc.

50. Neurotransmitter Receptors Channel-linked receptors –Ligand-gated ion channels –Action is immediate and brief –Excitatory receptors are channels for small cations Na + influx contributes most to depolarization –Inhibitory receptors allow Cl – influx that causes hyperpolarization © 2016 Pearson Education, Inc.

51. Figure 11.19 Channel-linked receptors cause rapid synaptic transmission. © 2016 Pearson Education, Inc. Ion flow blocked Ligand Ions flow Closed ion channel Open ion channel

52. Neurotransmitter Receptors (cont.) G protein–linked receptors –Responses are indirect, complex, slow, and often prolonged –Involves transmembrane protein complexes –Cause widespread metabolic changes –Examples: Muscarinic ACh receptors Receptors that bind biogenic amines Receptors that bind neuropeptides © 2016 Pearson Education, Inc.

53. Neurotransmitter Receptors (cont.) G protein–linked receptors (cont.) –Mechanism: Neurotransmitter binds to G protein–linked receptor, activating G protein Activated G protein controls production of second messengers, such as cyclic AMP, cyclic GMP, diacylglycerol, or Ca 2+ Second messengers can then: –Open or close ion channels –Activate kinase enzymes –Phosphorylate channel proteins –Activate genes and induce protein synthesis © 2016 Pearson Education, Inc.

54. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor Nucleus Receptor 1 Slide 2

55. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein GTP GDP GTP Receptor activates G protein. Nucleus Receptor 1 2 Slide 3

56. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein Adenylate cyclase GTP GDP GTP Receptor activates G protein. G protein activates adenylate cyclase. Nucleus Receptor 1 2 3 Slide 4

57. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein Adenylate cyclase ATP GTP GDP GTP Receptor activates G protein. G protein activates adenylate cyclase. Adenylate cyclase converts ATP to cAMP (2nd messenger). Nucleus Receptor cAMP 1 2 3 4 Slide 5

58. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein Adenylate cyclase Closed ion channel Open ion channel ATP GTP cAMP changes membrane permeability by opening or closing ion channels. GDP GTP Receptor activates G protein. G protein activates adenylate cyclase. Adenylate cyclase converts ATP to cAMP (2nd messenger). Nucleus Receptor cAMP 1 2 3 4 5a Slide 6

59. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein Adenylate cyclase Closed ion channel Open ion channel ATP GTP cAMP changes membrane permeability by opening or closing ion channels. GDP GTP cAMP activates enzymes. Receptor activates G protein. G protein activates adenylate cyclase. Adenylate cyclase converts ATP to cAMP (2nd messenger). Nucleus Active enzyme Receptor cAMP 1 2 3 4 5a 5b Slide 7

60. Figure 11.20 G protein–linked receptors cause the formation of intracellular second messengers. © 2016 Pearson Education, Inc. G protein signaling mechanisms are like a molecular relay race. Ligand (1st messenger) G protein Enzyme 2nd messenger Neurotransmitter (1st messenger) binds and activates receptor. Receptor G protein Adenylate cyclase Closed ion channel Open ion channel ATP GTP cAMP changes membrane permeability by opening or closing ion channels. cAMP activates specific genes. GDP GTP cAMP activates enzymes. Receptor activates G protein. G protein activates adenylate cyclase. Adenylate cyclase converts ATP to cAMP (2nd messenger). Nucleus Active enzyme Receptor cAMP 1 2 3 4 5a 5b 5c Slide 8

61. 11.10 Neural Integration Neural integration: neurons functioning together in groups Groups contribute to broader neural functions There are billions of neurons in CNS –Must have integration so that the individual parts fuse to make a smoothly operating whole © 2016 Pearson Education, Inc.

62. Organization of Neurons: Neuronal Pools Neuronal pool: functional groups of neurons –Integrate incoming information received from receptors or other neuronal pools –Forward processed information to other destinations © 2016 Pearson Education, Inc.

63. Organization of Neurons: Neuronal Pools (cont.) Simple neuronal pool –Single presynaptic fiber branches and synapses with several neurons in pool –Discharge zone: neurons closer to incoming fiber are more likely to generate impulse –Facilitated zone: neurons on periphery of pool are farther away from incoming fiber; usually not excited to threshold unless stimulated by another source © 2016 Pearson Education, Inc.

64. Figure 11.21 Simple neuronal pool. © 2016 Pearson Education, Inc. Presynaptic (input) fiber Facilitated zone Discharge zone Facilitated zone

65. Patterns of Neural Processing Serial processing –Input travels along one pathway to a specific destination One neuron stimulates next one, which stimulates next one, etc. –System works in all-or-none manner to produce specific, anticipated response –Best example of serial processing is a spinal reflex © 2016 Pearson Education, Inc.

66. Patterns of Neural Processing (cont.) Serial processing (cont.) –Reflexes Rapid, automatic responses to stimuli Particular stimulus always causes same response Occur over pathways called reflex arcs that have five components: –Receptor –Sensory neuron –CNS integration center –Motor neuron –Effector © 2016 Pearson Education, Inc.

67. Figure 11.22 A simple reflex arc. © 2016 Pearson Education, Inc. Stimulus Receptor Sensory neuron Integration center Motor neuron Effector Interneuron Spinal cord (CNS) Response 1 2 3 4 5

68. Patterns of Neural Processing (cont.) Parallel processing –Input travels along several pathways –Different parts of circuitry deal simultaneously with the information One stimulus promotes numerous responses –Important for higher-level mental functioning –Example: A sensed smell may remind one of an odor and any associated experiences © 2016 Pearson Education, Inc.

69. Types of Circuits Circuits: patterns of synaptic connections in neuronal pools Four types of circuits –Diverging –Converging –Reverberating –Parallel after-discharge © 2016 Pearson Education, Inc.

70. Figure 11.23a Types of circuits in neuronal pools. © 2016 Pearson Education, Inc. Input Diverging circuit One input, many outputs An amplifying circuit Example: A single neuron in the brain can activate 100 or more motor neurons in the spinal cord and thousands of skeletal muscle fibers Many outputs

71. Figure 11.23b Types of circuits in neuronal pools. © 2016 Pearson Education, Inc. Input 1 Input 2 Input 3 Converging circuit Many inputs, one output A concentrating circuit Example: Different sensory stimuli can all elicit the same memory Output

72. Figure 11.23c Types of circuits in neuronal pools. © 2016 Pearson Education, Inc. Input Reverberating circuit Signal travels through a chain of neurons, each feeding back to previous neurons An oscillating circuit Controls rhythmic activity Example: Involved in breathing, sleep-wake cycle, and repetitive motor activities such as walking Output

73. Figure 11.23d Types of circuits in neuronal pools. © 2016 Pearson Education, Inc. Input Output Parallel after-discharge circuit Signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell Impulses reach output cell at different times, causing a burst of impulses called an after-discharge Example: May be involved in exacting mental processes such as mathematical calculations

74. Developmental Aspects of Neurons Nervous system originates from neural tube and neural crest formed from ectoderm The neural tube becomes CNS –Neuroepithelial cells of neural tube proliferate into number of cells needed for development –Neuroblasts become amitotic and migrate –Neuroblasts sprout axons to connect with targets and become neurons © 2016 Pearson Education, Inc.

75. Developmental Aspects of Neurons Growth cone: prickly structure at tip of axon that allows it to interact with its environment via: –Cell surface adhesion proteins (laminin, integrin, and nerve cell adhesion molecules, or N-CAMs), which provide anchor points –Neurotropins that attract or repel the growth cone –Nerve growth factor (NGF), which keeps neuroblast alive –Filopodia are growth cone processes that follow signals toward target © 2016 Pearson Education, Inc.

76. Developmental Aspects of Neurons Once axon finds its target, it then must find right place to form synapse –Astrocytes provide physical support and the cholesterol needed for construction of synapses © 2016 Pearson Education, Inc.

77. Developmental Aspects of Neurons About two-thirds of neurons die before birth –If axons do not form a synapse with their target, they are triggered to undergo apoptosis (programmed cell death) –Many other cells also undergo apoptosis during development Neurons are amitotic after birth; however, there are a few special neuronal populations that continue to divide –Olfactory neurons and hippocampus © 2016 Pearson Education, Inc.

78. Figure 11.24 A neuronal growth cone. © 2016 Pearson Education, Inc.